It is proposed to investigate the aggregation pattern of bile salts in solutions by measuring the absolute estimates of the average degree of aggregation and polydispersity as a function of concentration of bile salts, ionic strength of solution, and temperature. We shall apply the techniques of sedimentation equilibrium, membrane osmometry, and light scattering radiance. The nonideal contributions and the effects of thermodynamic preferential interactions on measured degrees of aggregation will be evaluated by combining several approaches. By means of hydrodynamic measurements of sedimentation velocity, diffusion, and reduced viscosity, estimates of the hydrodynamic size of aggregates will be obtained. Hydrodynamic interaction parameters will also be evaluated. Evaluation of various interaction parameters in thermodynamic and hydrodynamic measurements is necessary in order to obtain the degrees of aggregation and size estimates at finite concentrations. A combined stopped-flow temperature-jump apparatus will be used for studies of the kinetics of aggregation in the dynamic range from a microsecond to a second. In order to use spectrophotometric absorption and fluorescence detection, a chromophoric moiety (for instance, tryptophan) will be coupled through peptide linkage to the side chain of bile salts leaving the steroid part intact. From the relaxation amplitudes, the thermodynamic parameters will be derived.